Various techniques have recently been proposed to effectively prevent data congestion in cellular communication systems. For example, the rapid proliferation of smartphones is a driving force behind a rise in the use of a large volume of mobile content. To distribute the load of an evolved Node B (eNB), Device-to-Device (D2D) communication between User Equipment (UEs) has been proposed. D2D communication can be conducted in a cellular communication system. A UE conducting D2D communication (hereinafter, referred to as a ‘D2D UE’) may operate as a UE conducting cellular communication (hereinafter, referred to as a ‘cellular UE’).
Typically, an eNB controls the transmission power of UEs to reduce interference from other cells, increase the battery lifespans of the UEs, and receive data and control information with appropriate power from the UEs within a cell managed by the eNB in the cellular communication system.
The eNB may notify the UEs of parameters needed for power control. The UEs may also estimate some parameters for power control on their own and set their transmission power based on these parameters. In this manner, the eNB measures parameters that may affect the UEs, such as channel qualities between the eNB and the UEs, reception signal strengths, or the like, with the aid of the UEs and reflects the parameters in power control for the UEs.
In typical cellular communication, an uplink receiver is a fixed eNB. Accordingly, an average noise and interference power received at the eNB from a neighbor cell may be measured over a long term. On the other hand, a receiver is a UE in D2D communication. Due to the mobility of the UE, it is difficult to measure average interference and noise ratios of neighbor UEs over a long term. As a result, power control for UEs in cellular communication is not viable for D2D communication. For example, in the case of D2D communication on an uplink of a cellular system (hereinafter, referred to as a ‘cellular uplink’), a transmitting D2D UE transmits a D2D communication signal on the cellular uplink and a receiving D2D UE receives the D2D communication signal on the cellular uplink. For power control for D2D communication, interference with an eNB caused by the transmitting D2D UE, interference with the receiving D2D UE caused by a cellular UE that transmits uplink data and control information, and interference with another receiving D2D UE caused by the transmitting D2D UE on the cellular uplink should be measured. As the number of channels to be measured increases, the amount of information to be exchanged for measuring the quality of the channels also increases, thereby increasing overhead. The increased overhead may become a serious problem in a D2D data multicast/broadcast scenario in which a transmitting D2D UE conducts D2D communication with multiple receiving D2D UEs. If a UE operates in Radio Resource Control (RRC)_IDLE mode, the UE should transmit a parameter for power control to the eNB to help the eNB to determine transmission power for the UEs. In this case, a Random Access (RA) procedure is additionally needed to switch RRC_IDLE-mode UEs to RRC_CONNECTED mode. Additional signaling involved in the RA procedure may cause overhead to the eNB. Considering that the D2D communication function may be executed in many other devices including home appliances such as a smart TV, a smart refrigerator, and the like, a laptop computer, a tablet Personal Computer (PC), and the like as well as a cellular device such as a smartphone, the overhead of RA signaling may impose a huge overhead on the eNB.
On the assumption that the quality of the afore-mentioned channels can be measured fully, a change may occur in the mobility of UEs including a D2D UE and a cellular UE and a pair of UEs for D2D communication at the moment when the already-measured channel quality values are reflected. The resulting channel mismatch may degrade system performance.
If D2D communication is conducted within a cell managed by an eNB, cellular communication resources may be shared as D2D communication resources according to an underlay scheme or time/frequency resources orthogonal to cellular communication resources may be used as D2D communication resources according to an overlay scheme. According to the underlay scheme, D2D communication interferes with legacy UEs conducting cellular communication, whereas according to the overlay scheme, D2D communication causes in-band emission or Inter-Carrier Interference (ICI)/Inter-Symbol Interference (ISI) to an eNB that receives cellular data or control information from legacy UEs.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.